Dehydrocyclization with an acidic multimetallic catalytic composite

ABSTRACT

Dehydrocyclizable hydrocarbons are converted to aromatics by contacting them at dehydrocyclization conditions with an acidic multimetallic catalytic composite comprising a combination of catalytically effective amounts of a platinum group component, a cobalt component, a lanthanide series component, and a halogen component with a porous carrier material. The platinum group, cobalt, lanthanide series and halogen components are present in the multimetallic catalyst in amounts respectively, calculated on an elemental basis, corresponding to about 0.01 to about 2 wt. % platinum group metal, about 0.05 to about 5 wt. % cobalt, about 0.01 to about 5 wt. % lanthanide series metal, and about 0.1 to about 3.5 wt. % halogen. Moreover, the catalytically active sites induced by these metallic components are uniformly dispersed throughout the porous carrier material and these metallic components are present in the catalyst in carefully controlled oxidation states such that substantially all of the platinum group component is in the elemental metallic state, substantially all of the lanthanide series component is in an oxidation state above that of the elemental metal, and substantially all of the catalytically available cobalt component is present in the elemental metallic state or in a state which is reducible to the elemental metallic state under dehydrocyclization conditions, or in a mixture of these states. A specific example of dehydrocyclization method disclosed herein is a method for converting a feed mixture of n-hexane and n-heptane to a product mixture of benzene and toluene which involves contacting the feed mixture and a hydrogen stream with the acidic multi-metallic catalyst disclosed herein at dehydrocyclization conditions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of my prior, copendingapplication Ser. No. 758,616 filed Jan. 12, 1977 (now U.S. Pat. No.4,087,381) which in turn is a division of my prior application Ser. No.633,890 filed Nov. 20, 1975 and issued May 17, 1977 as U.S. Pat. No.4,024,052. All of the teachings of these prior applications arespecifically incorporated herein by reference.

The subject of the present invention is, broadly, an improved method fordehydrocyclizing a dehydrocyclizable hydrocarbon to produce an aromatichydrocarbon. In a narrower aspect, the present invention involves amethod of dehydrocyclizing aliphatic hydrocarbons containing 6 to 20carbon atoms per molecule to monocyclic aromatic hydrocarbons withminimum production of side products such as C₁ to C₅ hydrocarbons,bicyclic aromatics, olefins and coke. In another aspect, the presentinvention relates to the dehydrocyclization use of an acidicmultimetallic catalytic composite comprising a combination ofcatalytically effective amounts of a platinum group component, a cobaltcomponent, a lanthanide series component, and a halogen component with aporous carrier material. This acidic multimetallic composite has beenfound to possess highly beneficial characteristics of activity,selectivity, and stability when it is employed in the dehydrocyclizationof dehydrocyclizable hydrocarbons to make aromatics such as benzene,toluene and xylene.

The conception of the present invention followed from my search for anovel catalytic composite possessing a hydrogenation-dehydrogenationfunction, a controllable cracking and isomerization function, andsuperior conversion, selectivity, and stability characteristics whenemployed in hydrocarbon conversion processes that have traditionallyutilized dual-function catalytic composites. In my prior applications, Idisclosed a significant finding with respect to a multimetalliccatalytic composite meeting these requirements. More specifically, Idetermined that a combination of specified amounts of a cobalt componentand a lanthanide series component can be utilized, under certainconditions, to beneficially interact with the platinum group componentof a dual-function acidic catalyst with a resultant marked improvementin the performance of such a catalyst. Now I have ascertained that anacidic multimetallic catalytic composite, comprising a combination ofcatalytically effective amounts of a platinum group component, a cobaltcomponent, a lanthanide series component and a halogen component with aporous carrier material, can have superior activity, selectivity, andstability characteristics when it is employed in a ring-closure ordehydrocyclization process if the catalytically active sites induced bythese components are uniformly dispersed in the porous carrier materialin the amounts specified hereinafter and if the oxidation state of theactive metallic ingredients are carefully controlled so thatsubstantially all of the platinum group component is present in theelemental metallic state, substantially all of the lanthanide seriescomponent is present in an oxidation state above that of the elementalmetal, and substantially all of the catalytically available cobaltcomponent is present in the elemental metallic state or in a state whichis reducible to the elemental metallic state under dehydrocyclizationconditions or in a mixture of these states.

The dehydrocyclization of dehydrocyclizable hydrocarbons is an importantcommercial process because of the great and expanding demand foraromatic hydrocarbons for use in the manufacture of various chemicalproducts such as synthetic fibers, insecticides, adhesives, detergents,plastics, synthetic rubbers, pharmaceutical products, high octanegasoline, perfumes, drying oils, ion-exchange resins, and various otherproducts well known to those skilled in the art. One example of thisdemand is in the manufacture of alkylated aromatics such asethylbenzene, cumene and dodecylbenzene by using the appropriatemono-olefins to alkylate benzene. Another example of this demand is inthe area of chlorination of benzene to give chlorobenzene which is thenused to prepare phenol by hydrolysis with sodium hydroxide. The chiefuse for phenol is of course in the manufacture of phenol-formaldehyderesins and plastics. Another route to phenol uses cumene as a startingmaterial and involves the oxidation of cumene by air to cumenehydroperoxide which can then be decomposed to phenol and acetone by theaction of an appropriate acid. The demand for ethylbenzene is primarilyderived from its use to manufacture styrene by selectivedehydrogenation; styrene is in turn used to make styrene-butadienerubber and polystyrene. Ortho-xylene is typically oxidized to phthalicanhydride by reaction in vapor phase with air in the presence of avanadium pentoxide catalyst. Phthalic anhydride is in turn used forproduction of plasticizers, polyesters and resins. The demand forpara-xylene is caused primarily by its use in the manufacture ofterephthalic acid or dimethyl terephthalate which in turn is reactedwith ethylene glycol and polymerized to yield polyester fibers.Substantial demand for benzene also is associated with its use toproduce aniline, Nylon, maleic anhydride, solvents and the likepetrochemical products. Toluene, on the other hand, is not, at leastrelative to benzene and the C₈ aromatics, in great demand in thepetrochemical industry as a basic building block chemical; consequently,substantial quantities of toluene are hydrodealkylated to benzene ordisproportionated to benzene and xylene. Another use for toluene isassociated with the transalkylation of trimethylbenzene with toluene toyield xylene.

Responsive to this demand for these aromatic products, the art hasdeveloped a number of alternative methods to produce them in commercialquantities. One method that has been widely studied involves theselective dehydrocyclization of a dehydrocyclizable hydrocarbon bycontacting the hydrocarbon with a suitable catalyst atdehydrocyclization conditions. As is the case with most catalyticprocedures, the principal measure of effectiveness for thisdehydrocyclization method involves the ability to perform its intendedfunction with minimum interference of side reactions for extendedperiods of time. The analytical terms used in the art to broadly measurehow well a particular catalyst performs its intended functions in aparticular hydrocarbon conversion reaction are activity, selectivity,and stability, and for purposes of discussion here, these terms aregenerally defined for a given reactant as follows: (1) activity is ameasure of the catalyst's ability to convert the hydrocarbon reactantinto products at a specified severity level where severity level meansthe specific reaction conditions used-- that is, the temperature,pressure, contact time, and presence of diluents such as H₂ ; (2)selectivity usually refers to the amount of desired product or productsobtained relative to the amount of the reactant charged or converted;(3) stability refers to the rate of change with time of the activity andselectivity parameters -- obviously the smaller rate implying the morestable catalyst. More specifically, in a dehydrocyclization process,activity commonly refers to the amount of conversion that takes placefor a given dehydrocyclizable hydrocarbon at a specified severity leveland is typically measured on the basis of disappearance of thedehydrocyclizable hydrocarbon; selectivity is typically measured by theamount, calculated on a weight percent of feed basis or on a molepercent of converted dehydrocyclizable hydrocarbon basis, of the desiredaromatic hydrocarbon or hydrocarbons obtained at the particular activityor severity level; and stability is typically equated to the rate ofchange with time of activity as measured by disappearance of thedehydrocyclizable hydrocarbon and of selectivity as measured by theamount of desired aromatic hydrocarbon produced. Accordingly, the majorproblem facing workers in the hydrocarbon dehydrocyclization orring-closure art is the development of a more active and selectivecatalytic composite that has good stability characteristics.

I have now found a dual-function acidic multimetallic catalyticcomposite which possesses improved activity, selectivity, and stabilitywhen it is employed in a process for the dehydrocyclization ofdehydrocyclizable hydrocarbons. In particular, I have determined thatthe use of an acidic multimetallic catalyst, comprising a combination ofcatalytically effective amounts of a platinum group component, a cobaltcomponent, a lanthanide series component, and a halogen component with aporous refractory carrier material, can enable the performance of adehydrocyclization process to be substantially improved if thecatalytically active sites induced by the metallic components areuniformly dispersed throughout the carrier material in the amounts andrelative relationships specified hereinafter and if their oxidationstates of the active metallic ingredients are carefully controlled to bein the states hereinafter specified. Moreover, particularly good resultsare obtained when this catalyst is prepared and maintained, during usein the dehydrocyclization method, in a substantially sulfur-free state.This acidic multimetallic catalytic composite is particularly useful inthe dehydrocyclization of C₆ to C₁₀ paraffins to produce aromatichydrocarbons such as benzene, toluene, and the xylenes with minimizationof by-products such as C₁ to C₅ saturated hydrocarbons, bicyclicaromatics, olefins and coke.

In sum, the current invention involves the significant finding that acombination of a cobalt component and a lanthanide series component canbe utilized under the circumstances specified herein to beneficiallyinteract with and promote an acidic dehydrocyclization catalystcontaining a platinum group metal when it is used in the production ofaromatics by ring-closure of aliphatic hydrocarbons.

It is, accordingly, one object of the present invention to provide anovel method for the dehydrocyclization of dehydrocyclizablehydrocarbons utilizing an acidic multimetallic catalytic compositecomprising catalytically effective amounts of a platinum groupcomponent, a cobalt component, a lanthanide series component and ahalogen component combined with a porous carrier material. A secondobject is to provide a novel acidic catalytic composite having superiorperformance characteristics when utilized in a dehydrocyclizationprocess. Another object is to provide an improved method for thedehydrocyclization of paraffin hydrocarbons to produce aromatichydrocarbons which method minimizes undesirable by-products such as C₁to C₅ saturated hydrocarbons, bicyclic aromatics, olefins and coke.

In brief summary, one embodiment of the present invention involves amethod for dehydrocyclizing a dehydrocyclizable hydrocarbon whichcomprises contacting the hydrocarbon at dehydrocyclization conditionswith an acidic multimetallic catalytic composite comprising a porouscarrier material containing a uniform dispersion of catalyticallyeffective amounts of a platinum group component, a cobalt component, alanthanide series component, and a halogen component. Moreover,substantially all of the platinum group component is present in thecomposite in the elemental metallic state, substantially all of thelanthanide series component is present in a positive oxidation state,and substantially all of the catalytically available cobalt component ispresent in the elemental metallic state or in a state which is reducibleto the elemental metallic state under dehydrocyclization conditions orin a mixture of these states. Further these components are present inthis composite in amounts, calculated on an elemental basis, sufficientto result in the composite containing about 0.01 to about 2 wt. %platinum group metal, about 0.05 to about 5 wt. % cobalt, about 0.01 toabout 5 wt. % lanthanide series metal and about 0.1 to about 3.5 wt. %halogen.

A second embodiment relates to the dehydrocyclization method describedin the first embodiment wherein the dehydrocyclizable hydrocarbon is analiphatic hydrocarbon containing 6 to 20 carbon atoms per molecule.

A highly preferred embodiment comprehends the dehydrocyclization methodcharacterized in the first embodiment wherein the catalyst is preparedand maintained in a sulfur-free state and wherein the contacting isperformed in a substantially sulfur-free environment.

Another embodiment relates to the catalytic composite used in the first,second or third embodiments and involves the further limitation that thehalogen component is combined chloride.

Other objects and embodiments of the present invention involve specificdetails regarding essential and preferred catalytic ingredients,preferred amounts of ingredients, suitable methods of multimetalliccomposite preparation, suitable dehydrocyclizable hydrocarbons,operating conditions for use in the dehydrocyclization process, and thelike particulars. There are hereinafter given in the following detaileddiscussion of each of these facets of the present invention.

Regarding the dehydrocyclizable hydrocarbon that is subjected to themethod of the present invention, it can in general be any aliphatichydrocarbon or substituted aliphatic hydrocarbon capable of undergoingring-closure to produce an aromatic hydrocarbon. That is, it is intendedto include within the scope of the present invention, thedehydrocyclization of any organic compound capable of undergoingring-closure to produce an aromatic hydrocarbon containing the same, orless than the same, number of carbon atoms than the reactant compoundand capable of being vaporized at the dehydrocyclization temperaturesused herein. More particularly, suitable dehydrocyclizable hydrocarbonsare: aliphatic hydrocarbons containing 6 to 20 carbon atoms per moleculesuch as C₆ to C₂₀ paraffins, C₆ to C₂₀ olefins and C₆ to C₂₀polyolefins. Specific examples of suitable dehydrocyclizablehydrocarbons are: (1) paraffins such as n-hexane, 2-methylpentane,3-methylpentane, 2,2-dimethylbutane, n-heptane, 2-methylhexane,3-ethylpentane, 2,2-dimethylpentane, n-octane, 2-methylheptane,3-ethylhexane, 2,2-dimethylhexane, 2-methyl-3-ethylpentane,2,2,3-trimethylpentane, n-nonane, 2-methyloctane, 2,2-dimethylheptane,n-decane and the like compounds; (2) olefins such as 1-hexene,2-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene and the likecompounds; and, (3) diolefins such as 1,5-hexadiene,2-methyl-2,4-hexadiene, 2,6-octadiene and the like diolefins.

In a preferred embodiment, the dehydrocyclizable hydrocarbon is aparaffin hydrocarbon having about 6 to 10 carbon atoms per molecule. Forexample, paraffin hydrocarbons containing about 6 to 8 carbon atoms permolecule are dehydrocyclized by the subject method to produce thecorresponding aromatic hydrocarbon. It is to be understood that thespecific dehydrocyclizable hydrocarbons mentioned above can be chargedto the present method individually, in admixture with one or more of theother dehydrocyclizable hydrocarbons, or in admixture with otherhydrocarbons such as naphthenes, aromatics, C₁ to C₅ paraffins and thelike. Thus mixed hydrocarbon fractions, containing significantquantities of dehydrocyclizable hydrocarbons that are commonly availablein a typical refinery, are suitable charge stocks for the instantmethod; for example, highly paraffinic straight run naphthas, paraffinicraffinates from aromatic extraction or adsorption, C₆ to C₉paraffin-rich streams and the like refinery streams. An especiallypreferred embodiment involves a charge stock which is a paraffin-richnaphtha fraction boiling in the range of about 140° to about 400° F.Generally, best results are obtained with a charge stock comprising amixture of C₆ to C₉ paraffins, and especially C₆ to C₉ normal paraffins.

The acidic multimetallic catalyst used in the present dehydrocyclizationmethod comprises a porous carrier material having combined therewithcatalytically effective amounts of a platinum group component, a cobaltcomponent, a lanthanide series component, and a halogen component.

Considering first the porous carrier material utilized in the presentinvention, it is preferred that the material be a porous, adsorptive,high-surface area support having a surface area of about 25 to about 500m² /g. The porous carrier material should be relatively refractory tothe conditions utilized in the hydrocarbon conversion process, and it isintended to include within the scope of the present invention carriermaterials which have traditionally been utilized in dual-functionhydrocarbon conversion catalysts such as: (1) activated carbon, coke, orcharcoal; (2) silica or silica gel, silicon carbide, clays, andsilicates including those synthetically prepared and naturallyoccurring, which may or may not be acid treated for example, attapulgusclay, china clay, diatomaceous earth, fuller's earth, kaolin,kieselguhr, etc.; (3) ceramics, porcelain, crushed firebrick, bauxite;(4) refractory inorganic oxides such as alumina, titanium dioxide,zirconium dioxide, chromium oxide, beryllium oxide, vanadium oxide,cesium oxide, hafnium oxide, zinc oxide, magnesia, boria, thoria,silica-alumina, silica-magnesia, chromia-alumina, alumina-boria,silica-zirconia, etc.; (5) crystalline zeolitic aluminosilicates such asnaturally occurring or synthetically prepared mordenite and/orfaujasite, either in the hydrogen form or in a form which has beentreated with multivalent cations; (6) spinels such as MgAl₂ O₄, FeAl₂O₄, ZnAl₂ O₄, MnAl₂ O₄, CaAl₂ O₄, and other like compounds having theformula MO.Al₂ O₃ where M is a metal having a valence of 2; and (7)combinations of elements from one or more of these groups. The preferredporous carrier materials for use in the present invention are refractoryinorganic oxides, with best results obtained with an alumina carriermaterial. Suitable alumina materials are the crystalline aluminas knownas gamma-, eta, and theta-alumina, with gamma- or eta-alumina givingbest results. In addition, in some embodiments the alumina carriermaterial may contain minor proportions of other well known refractoryinorganic oxides such as silica, zirconia, magnesia, etc.; however, thepreferred support is substantially pure gamma- or eta-alumina. Preferredcarrier materials have an apparent bulk density of about 0.3 to about0.8 g/cc and surface area characteristics such that the average porediameter is about 20 to 300 Angstroms, the pore volume is about 0.1 toabout 1 cc/g and the surface area is about 100 to about 500 m² /g. Ingeneral, best results are typically obtained with a gamma-aluminacarrier material which is used in the form of spherical particleshaving: a relatively small diameter (i.e. typically about 1/16 inch), anapparent bulk density of about 0.3 to about 0.8 g/cc, a pore volume ofabout 0.4 ml/g, and a surface area of about 150 to about 250 m² /g.

The preferred alumina carrier material may be prepared in any suitablemanner and may be synthetically prepared or natural occurring. Whatevertype of alumina is employed, it may be activated prior to use by one ormore treatments including drying, calcination, steaming, etc., and itmay be in a form known as activated alumina, activated alumina ofcommerce, porous alumina, alumina gel, etc. For example, the aluminacarrier may be prepared by adding a suitable alkaline reagent, such asammonium hydroxide, to a salt of aluminum such as aluminum chloride,aluminum nitrate, etc., in an amount to form an aluminum hydroxide gelwhich upon drying and calcining is converted to alumina. The aluminacarrier may be formed in any desired shape such as spheres, pills,cakes, extrudates, powders, granules, tablets, etc., and utilized in anydesired size. For the purpose of the present invention a particularlypreferred form of alumina is the sphere, and alumina spheres may becontinuously manufactured by the well-known oil drop method whichcomprises: forming an alumina hydrosol by any of the techniques taughtin the art and preferably by reacting aluminum metal with hydrochloricacid, combining the resultant hydrosol with a suitable gelling agent anddropping the resultant mixture into an oil bath maintained at elevatedtemperatures. The droplets of the mixture remain in the oil bath untilthey set and form hydrogel spheres. The spheres are then continuouslywithdrawn from the oil bath and typically subjected to specific agingtreatments in oil and an ammoniacal solution to further improve theirphysical characteristics. The resulting aged and gelled particles arethen washed and dried at a relatively low temperature of about 300° F.to about 400° F. and subjected to a calcination procedure at atemperature of about 850° F. to about 1300° F. for a period of about 1to about 20 hours. This treatment effects conversion of the aluminahydrogel to the corresponding crystalline gamma-alumina. See theteachings of U.S. Pat. No. 2,620,314 for additional details.

The expression "catalytically available cobalt" as used herein isintended to mean the portion of the cobalt component of the subjectcatalytic composite that is available for use in accelerating thedehydrocyclization reaction of interest. For purposes of the presentinvention, it is highly preferred that the catalytically availablecobalt comprise at least about 10% of the total cobalt content of thecatalyst and, even more preferably, at least about 50% thereof. Forcertain types of carrier materials which can be used in the preparationof the instant catalyst composite, it has been observed that a portionof the cobalt incorporated therein is essentially bound-up in thecrystal structure thereof in a manner which essentially makes itcatalytically unavailable; in fact, it is more a part of the refractorycarrier material than a catalytically active component. Specificexamples of this effect are observed when the carrier material can forma refractory spinel or spinel-like structure with a portion of thecobalt component and/or when a refractory cobalt oxide or aluminate isformed by reaction of the carrier material (or precursors thereof) witha portion of the cobalt component. When this effect occurs, it is onlywith great difficulty that the portion of the cobalt bound-up with thesupport can be reduced to a catalytically active state and theconditions required to do this are beyond the severity levels normallyassociated with hydrocarbon conversion conditions and are in fact likelyto seriously damage the necessary porous characteristics of the support.In the cases where cobalt can interact with the crystal structure of thesupport to render a portion thereof catalytically unavailable, theconcept of the present invention merely requires that the amount ofcobalt added to the subject catalyst be adjusted to satisfy therequirements of the support as well as the catalytically availablecobalt requirements of the present invention. Against this background,then, the hereinafter stated specifications for oxidation state anddispersion of the cobalt component are to be interpreted as directed toa description of the catalytically available cobalt. On the other hand,the specifications for the amount of cobalt used are to be interpretedto include all of the cobalt contained in the catalyst in any form.

One essential ingredient of the present catalytic composite is alanthanide series component. By the use of the generic expression"lanthanide series component" it is intended to cover the 15 innertransition metallic elements and mixtures thereof that are commonlyknown as the "lanthanide series metals" or "rare earth metals."Specifically, included within this definition are the followingelements: lanthanum, cerium, praseodymium, neodymium, promethium,samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium,thulium, ytterbium and lutetium. This component may be present in theinstant multimetallic composite in any form wherein substantially all ofthe lanthanide series metal is present in an oxidation state above thatof the corresponding metal such as in chemical combination with one ormore of the other ingredients of the composite, or as a chemicalcompound such as a lanthanide oxide, halide, oxyhalide, aluminate, andthe like. However, best results are believed to be obtained whensubstantially all of the lanthanide series component exists in the formof the corresponding oxide and the subsequently described oxidation andprereduction procedure is believed, on the basis of the availableevidence, to result in this condition. This lanthanide series componentmay be utilized in the composite in any amount which is catalyticallyeffective, with the preferred amount being about 0.01 to about 5 wt. %thereof, calculated on an elemental basis. Typically, best results areobtained with about 0.05 to about 2 wt. % lanthanide series metal.According to one embodiment of the present invention, it is anespecially preferred practice to select the specific amount oflanthanide series element from within this broad weight range as afunction of the amount of the platinum group component, on an atomicbasis, as is explained hereinafter. The lanthanide series elements thatare especially preferred for purposes of the present invention arelanthanum, cerium, and neodymium, with neodymium giving best results.

The lanthanide series component may be incorporated into the catalyticcomposite in any suitable manner known to those skilled in the catalystformulation art which ultimately results in a uniform dispersion of thelanthanide series moiety in the carrier material. In addition, it may beadded at any stage of the preparation of the composite--either duringpreparation of the carrier material or thereafter--and the precisemethod of incorporation used is not deemed to be critical. However, bestresults are obtained when the lanthanide series component isincorporated in a manner such that is relatively uniformly distributedthroughout the carrier material in a positive oxidation state or a statewhich is easily converted to a positive oxidation state in thesubsequently described oxidation step. One preferred procedure forincorporating this component into the composite involves cogelling orcoprecipitating the lanthanide series component during the preparationof the preferred carrier material, alumina. This procedure usuallycomprehends the addition of a soluble, decomposable compound of alanthanide series element such as neodymium nitrate to the aluminahydrosol before it is gelled. The resulting mixture is then finished byconventional gelling, aging, drying and calcination steps as explainedhereinbefore. Another preferred way of incorporating this component isan impregnation step wherein the porous carrier material is impregnatedwith a suitable lanthanide series compound-containing solution eitherbefore, during or after the carrier material is calcined. Preferredimpregnation solutions are aqueous solutions of water-soluble,decomposable lanthanide series compounds such as a lanthanide acetate, alanthanide bromide, a lanthanide perchlorate, a lanthanide chloride, alanthanide iodide, a lanthanide nitrate, and the like compounds. Bestresults are ordinarily obtained when the impregnation solution is anaqueous solution of a lanthanide chloride or a lanthanide nitrate. Thislanthanide series component can be added to the carrier material, eitherprior to, simultaneously with, or after the other metallic componentsare combined therewith. Best results are usually achieved when thiscomponent is added simultaneously with the other metallic components. Infact, the preferred preparation procedure for the instant catalystinvolves a one step impregnation procedure with an acidic aqueousimpregnation solution containing the deemed amounts of chloroplatinicacid, a lanthanide nitrate, a cobaltous chloride and hydrochloric acid.

A second essential ingredient of the subject catalyst is the platinumgroup component. That is, it is intended to cover the use of platinum,iridium, osmium, ruthenium, rhodium, palladium, or mixtures thereof, asa second component of the present composite. It is an essential featureof the present invention that substantially all of this platinum groupcomponent exists within the final catalytic composite in the elementalmetallic state. Generally, the amount of this component present in thefinal catalytic composite is small compared to the quantities of theother components combined therewith. In fact, the platinum groupcomponent generally will comprise about 0.01 to about 2 wt. % of thefinal catalytic composite, calculated on an elemental basis. Excellentresults are obtained when the catalyst contains about 0.05 to about 1wt. % of platinum, iridium, rhodium, or palladium metal. Particularlypreferred mixtures of these metals are platinum and iridium, andplatinum and rhodium.

This platinum group may be incorporated in the catalytic composite inany suitable manner known to result in a relatively uniform distributionof this component in the carrier material such as coprecipitation orcogelation, ion exchange or impregnation. The preferred method ofpreparing the catalyst involves the utilization of a soluble,decomposable compound of platinum group metal to impregnate the carriermaterial in a relatively uniform manner. For example, this component maybe added to the support by commingling the latter with an aqueoussolution of chloroplatinic or chloroiridic or chloropalladic acid. Otherwater-soluble compounds or complexes of platinum group metals may beemployed in impregnation solutions and include ammonium chloroplatinate,bromoplatinic acid, platinum trichloride, platinum tetrachloridehydrate, platinum dichlorocarbonyl dichloride, dinitrodiaminoplatinum,sodium tetranitroplatinate (II), palladium chloride, palladium nitrate,palladium sulfate, diamminepalladium (II) hydroxide, tetramminepalladium(II) chloride, hexamminerhodium chloride, rhodium carbonylchloride,rhodium trichloride hydrate, rhodium nitrate, sodium hexachlororhodate(III), sodium hexanitrorhodate (III), iridium tribromide, iridiumdichloride, iridium tetrachloride, sodium hexanitroiridate (III),potassium or sodium chloroiridate, potassium rhodium oxalate, etc. Theutilization of a platinum, iridium, rhodium, or palladium chloridecompound, such as chloroplatinic, chloroiridic, or chloropalladic acidor rhodium trichloride hydrate, is preferred since it facilitates theincorporation of both the platinum group components and at least a minorquantity of the halogen component in a single step. Hydrogen chloride orthe like acid is also generally added to the impregnation solution inorder to further facilitate the incorporation of the halogen componentand the uniform distribution of the metallic components throughout thecarrier material. In addition, it is generally preferred to impregnatethe carrier material after it has been calcined in order to minimize therisk of washing away the valuable platinum or palladium compounds;however, in some cases it may be advantageous to impregnate the carriermaterial when it is in a gelled state.

A third essential ingredient of the acidic multimetallic catalyticcomposite used in the present invention is a cobalt component. Althoughthis component may be initially incorporated into the composite in manydifferent decomposable forms which are hereinafter stated, my basicfinding is that the catalytically active state for hydrocarbonconversion with this component is the elemental metallic state.Consequently, it is a feature of my invention that substantially all ofthe catalytically available cobalt component exists in the catalyticcomposite either in the elemental metallic state or in a state which isreducible to the elemental state under dehydrocyclization conditions orin a mixture of these states. Examples of this last state are obtainedwhen the catalytically available cobalt component is initially presentin the form of cobalt oxide, hydroxide, halide, oxyhalide, and the likereducible compounds. As a corollary to this basic finding on the activestate of the catalytically available cobalt component, it follows thatthe presence of the catalytically available cobalt in forms which arenot reducible at dehydrocyclization conditions is to be scrupulouslyavoided if the full benefits of the present invention are to berealized. Illustrative of these undesired forms are cobalt sulfide andthe cobalt oxysulfur compounds such as cobalt sulfate. Best results areobtained when the composite initially contains all of the catalyticallyavailable cobalt component in the elemental metallic state or in areducible oxide state or in a mixture of these states. All availableevidence indicates that the preferred preparation procedure specificallydescribed in Example I results in a catalyst having the catalyticallyavailable cobalt component in the elemental metal form and/or in areducible oxide form. Based on the performance of such a catalyst, it isbelieved that substantially all of this reducible oxide form of thecobalt component is reduced to the elemental metallic state when adehydrocyclization process using this catalyst is started-up andlined-out at dehydrocyclization conditions. The cobalt component may beutilized in the composite in any amount which is catalyticallyeffective, with the preferred amount being about 0.05 to about 5 wt. %thereof, calculated on an elemental cobalt basis. Typically, bestresults are obtained with about 0.1 to about 2.5 wt. % cobalt. It is,additionally, preferred to select the specific amount of cobalt fromwithin this broad weight range as a function of the amount of theplatinum group component, on an atomic basis, as is explainedhereinafter.

The cobalt component may be incorporated into the catalytic composite inany suitable manner known to those skilled in the catalyst formulationart to result in a relatively uniform distribution of the catalyticallyavailable cobalt in the carrier material such as coprecipitation,cogelation, ion exchange, impregnation, etc. In addition, it may beadded at any stage of the preparation of the composite -- either duringpreparation of the carrier material or thereafter -- since the precisemethod of incorporation used is not deemed to be critical. However, bestresults are obtained when the catalytically available cobalt componentis relatively uniformly distributed throughout the carrier material in arelatively small particle or crystallite size having a maximum dimensionof less than 100 Angstroms, and the preferred procedures are the onesthat are known to result in a composite having a relatively uniformdistribution of the catalytically available cobalt moiety in arelatively small particle size. One acceptable procedure forincorporating this component into the composite involves cogelling orcoprecipitating the cobalt component during the preparation of thepreferred carrier material, alumina. This procedure usually comprehendsthe addition of a soluble, decomposable, and reducible compound ofcobalt such as cobalt chloride, acetate or nitrate to the aluminahydrosol before it is gelled. Alternatively, the reducible compound ofcobalt can be added to the gelling agent before it is added to thehydrosol. The resulting mixture is then finished by conventionalgelling, aging, drying, and calcination steps as explained hereinbefore.One preferred way of incorporating this component is an impregnationstep wherein the porous carrier material is impregnated with a suitablecobalt-containing solution either before, during, or after the carriermaterial is calcined or oxidized. The solvent used to form theimpregnation solution may be water, alcohol, ether, or any othersuitable organic or inorganic solvent provided the solvent does notadversely interact with any of the other ingredients of the composite orinterfere with the distribution and reducton of the cobalt component.Preferred impregnation solutions are aqueous solutions of water-soluble,decomposable, and reducible cobalt compounds such as cobaltous acetate,cobaltous benzoate, cobaltous bromate, cobaltous bromide, cobaltouschlorate and perchlorate, cobaltous chloride, cobaltic chloride,cobaltous fluoride, cobaltous iodide, cobaltous nitrate, hexamminecobalt(III) chloride, hexamminecobalt (III) nitrate, triethylenediamminecobalt(III) chloride, cobaltous hexamethylenetetramine, and the likecompounds. Best results are ordinarily obtained when the impregnationsolution is an aqueous solution of cobalt chloride or acetate ornitrate. This cobalt component can be added to the carrier material,either prior to, simultaneously with, or after the other metalliccomponents are combined therewith. Best results are usually achievedwhen this component is added simultaneously with the platinum group andlanthanide series components via an acidic aqueous impregnationsolution. In fact, excellent results are obtained, as reported in theexamples, with an impregnation procedure using an acidic aqueoussolution comprising chloroplatinic acid, cobaltous chloride, andhydrochloric acid.

It is essential to incorporate a halogen component into the acidicmultimetallic catalytic composite used in the present invention.Although the precise form of the chemistry of the association of thehalogen component with the carrier material is not entirely known, it iscustomary in the art to refer to the halogen component as being combinedwith the carrier material, or with the other ingredients of the catalystin the form of the halide (e.g. as the chloride). This combined halogenmay be either fluorine, chlorine, iodine, bromine, or mixtures thereof.Of these, fluorine and, particularly, chlorine are preferred for thepurposes of the present invention. The halogen may be added to thecarrier material in any suitable manner, either during preparation ofthe support or before or after the addition of the other components. Forexample, the halogen may be added, at any stage of the preparation ofthe carrier material or to the calcined carrier material, as an aqueoussolution of a suitable, decomposable halogen-containing compound such ashydrogen fluoride, hydrogen chloride, hydrogen bromide, ammoniumchloride, etc. The halogen component or a portion thereof, may becombined with the carrier material during the impregnation of the latterwith the platinum group, cobalt, or lanthanide series components; forexample, through the utilization of a mixture of chloroplatinic acid andhydrogen chloride. In another situation, the alumina hydrosol which istypically utilized to form the preferred alumina carrier material maycontain halogen and thus contribute at least a portion of the halogencomponent to the final composite. For the dehydrocyclization reaction,the halogen will be typically combined with the carrier material in anamount sufficient to result in a final composite that contains about 0.1to about 3.5%, and preferably about 0.5 to about 1.5%, by weight ofhalogen, calculated on an elemental basis. It is to be understood thatthe specified level of halogen component in the instant catalyst can beachieved or maintained during use in the dehydrocyclization ofhydrocarbons by continuously or periodically adding to the reaction zonea decomposable halogen-containing compound such as an organic chloride(e.g., ethylene dichloride, carbon tetrachloride, t-butyl chloride) inan amount of about 1 to 100 wt. ppm. of the hydrocarbon feed, andpreferably, about 1 to 10 wt. ppm.

Regarding especially preferred amounts of the various metalliccomponents of the subject catalyst, I have found it to be an excellentpractice to specify the amounts of the cobalt component and thelanthanide series component as a function of the amount of the platinumgroup component. On this basis, the amount of the cobalt component isordinarily selected so that the atomic ratio of cobalt to platinum groupmetal contained in the composite is about 0.1:1 to about 66:1, with thepreferred range being about 0.4:1 to about 18:1. Similarly, the amountof the lanthanide series component is ordinarily selected to produce acomposite containing an atomic ratio of lanthanide series metal toplatinum group metal of about 0.1:1 to about 20:1, with the preferredrange being about 1:1 to about 10:1.

Another significant parameter for the instant catalyst is the "totalmetals content" which is defined to be the sum of the platinum groupcomponent, the cobalt component, and the lanthanide series component,calculated on an elemental basis. Good results are ordinarily obtainedwith the subject catalyst when this parameter is fixed at a value ofabout 0.15 to about 4 wt. %, with best results ordinarily achieved at ametals loading of about 0.3 to about 3 wt. %.

Regardless of the details of how the components of the catalyst arecombined with the porous carrier material, the final catalyst generallywill be dried at a temperature of about 200° to about 600° F. for aperiod of at least about 2 to about 24 hours or more, and finallycalcined or oxidized at a temperature of about 700° F. to about 1100° F.in an air to oxygen atmosphere for a period of about 0.5 to about 10hours in order to convert substantially all of the metallic componentsto the corresponding oxide form. Because a halogen component is utilizedin the catalyst, best results are generally obtained when the halogencontent of the catalyst is adjusted during the oxidation step byincluding a halogen or a halogen-containing compound such as HCl or anHCl-producing substance in the air or oxygen atmosphere utilized. Inparticular, when the halogen component of the catalyst is chlorine, itis preferred to use a mole ratio of H₂ O to HCl of about 5:1 to about100:1 during at least a portion of the oxidation step in order to adjustthe final chlorine content of the catalyst to a range of about 0.1 toabout 3.5 wt. %. Preferably, the duration of this halogenation step isabout 1 to 5 hours.

The resultant oxidized catalytic composite is preferably subjected to asubstantially water-free reduction step prior to its use in thedehydrocyclization of hydrocarbons. This step is designed to selectivelyreduce the platinum group component to the elemental metallic state,while maintaining the lanthanide series component in a positiveoxidation state, and to insure a uniform and finely divided dispersionof the metallic components throughout the carrier material. Preferably,a substantially pure and dry hydrogen stream (i.e. less than 20 vol.ppm. H₂ O) is used as the reducing agent in this step. The reducingagent is contacted with the oxidized catalyst at conditions including areduction temperature of about 400° F. to about 1200° F., a gas hourlyspace velocity sufficient to rapidly dissipate any local concentrationsof water formed during the reduction procedure, and a period of time ofabout 0.5 to 10 hours effective to reduce substantially all of theplatinum group component to the elemental metallic state, whilemaintaining the lanthanide series component in a positive oxidationstate. If this reduction step is performed with a hydrocarbon-freehydrogen stream at the temperature indicated, and if the catalyticallyavailable cobalt component is properly distributed in the carriermaterial in the oxide form and in the specified particle size, asubstantial amount of the catalytically available cobalt component maynot be reduced in this step. However, once the catalyst sees a mixtureof hydrogen and hydrocarbon (such as during the start-up and lining-outof the dehydrocyclization process using same), at least a major portionand typically substantially all of the catalytically available cobaltcomponent is quickly reduced at the specified reduction temperaturerange. This reduction treatment may be performed in situ as part of astart-up sequence if precautions are taken to predry the plant to asubstantially water-free state and if a substantially water-freehydrogen stream is used.

The resulting selectively reduced catalytic composite is, in accordancewith the basic concept of the present invention, preferably maintainedin a sulfur-free state both during its preparation and thereafter duringits use in the dehydrocyclization of hydrocarbons. As indicatedpreviously, the beneficial interaction of the catalytically availablecobalt component with the other ingredients of the present catalyticcomposite is contingent upon the maintenance of the cobalt moiety in ahighly dispersed, readily reducible state in the carrier material.Sulfur in the form of sulfide adversely interferes with both thedispersion and reducibility of the catalytically available cobaltcomponent and consequently it is a highly preferred practice to avoidpresulfiding the selectively reduced acidic multimetallic catalystresulting from the reduction step. Once the catalyst has been exposed tohydrocarbon for a sufficient period of time to lay down a protectivelayer of carbon or coke on the surface thereof, the sulfur sensitivityof the resulting carbon-containing composite changes rather markedly andthe presence of small amounts of sulfur can be tolerated withoutpermanently disabling the catalyst. The exposure of the freshly reducedcatalyst to sulfur can seriously damage the cobalt component thereof andconsequently, jeopardize the superior performance characteristicsassociated therewith. However, once a protective layer of carbon isestablished on the catalyst, the sulfur deactivation effect is lesspermanent and sulfur can be purged therefrom by exposure to asulfur-free hydrogen stream at a temperature of about 800° to 1100° F.

According to the present invention, the dehydroxcyclizable hydrocarbonis contacted with the instant acidic multimetallic catalyst in adehydrocyclization zone maintained at dehydrocyclization conditions.This contacting may be accomplished by using the catalyst in a fixed bedsystem, a moving bed system, a fluidized bed system, or in a batch typeoperation; however, in view of the danger of attrition losses of thevaluable catalyst and of well-known operational advantages, it ispreferred to use either a fixed bed system or a dense-phase moving bedsystem such as is shown in U.S. Pat. No. 3,725,249. It is alsocontemplated that the contacting step can be performed in the presenceof a physical mixture of particles of the catalyst of the presentinvention and particles of a conventional dual-function catalyst of theprior art. In a fixed bed system, the dehydrocyclizablehydrocarbon-containing charge stock is preheated by any suitable heatingmeans to the desired reaction temperature and then passed into adehydrocyclization zone containing a fixed bed of the acidicmultimetallic catalyst. It is, of course, understood that thedehydrocyclization zone may be one or more separate reactors withsuitable means therebetween to ensure that the desired conversiontemperature is maintained at the entrance to each reactor. It is alsoimportant to note that the reactants may be contacted with the catalystbed in either upward, downward, or radial flow fashion with the latterbeing preferred. In addition, the reactants may be in the liquid phase,a mixed liquid-vapor phase, or a vapor phase when they contact thecatalyst, with best results obtained in the vapor phase. Thedehydrocyclization system then preferably comprises a dehydrocyclizationzone containing one or more fixed beds or dense-phase moving beds of theinstant catalyst. In a multiple bed system, it is, of course, within thescope of the present invention to use the present catalyst in less thanall of the beds with a conventional dual-function catalyst being used inthe remainder of the beds. This dehydrocyclization zone may be one ormore separate reactors with suitable heating means therebetween tocompensate for the endothermic nature of the dehydrocyclization reactionthat takes place in each catalyst bed.

Although hydrogen is the preferred diluent for use in the subjectdehydrocyclization method, in some cases other art-recognized diluentsmay be advantageously utilized, either individually or in admixture withhydrogen, such as C₁ to C₅ paraffins such as methane, ethane, propane,butane and pentane; carbon dioxide, the like diluents, and mixturesthereof. Hydrogen is preferred because it serves the dual-function ofnot only lowering the partial pressure of the dehydrocyclizablehydrocarbon, but also of suppressing the formation ofhydrogen-deficient, carbonaceous deposits (commonly called coke) on thecatalytic composite. Ordinarily, hydrogen is utilized in amountssufficient to insure a hydrogen to hydrocarbon mole ratio of about 0.1:1to about 10:1, with best results obtained in the range of about 0.5:1 toabout 5:1. The hydrogen stream charged to the dehydrocyclization zonewill typically be recycle hydrogen obtained from the effluent streamfrom this zone after a suitable hydrogen separation step.

Since sulfur has a high affinity for cobalt at dehydrocyclizationconditions, I have found that best results are achieved in adehydrocyclization method using the instant acidic multimetalliccatalytic composite when the catalyst is used in a substantiallysulfur-free environment. The expression "substantially sulfur-freeenvironment" is intended to mean that the total amount (expressed asequivalent elemental sulfur) of sulfur or sulfur-containing compounds,which are capable of producing a metallic sulfide at the reactionconditions used, entering the dehydrocyclization zone containing theinstant catalyt from any source is continuously maintained at an amountequivalent to less than 10 wt. ppm. of the hydrocarbon charge stock,more preferably less than 5 wt. ppm., and most preferably less than 1wt. ppm. Since in the ordinary operation of the subjectdehydrocyclization method the influent hydrogen stream is autogenouslyproduced, the prime source for any sulfur entering thedehydrocyclization zone is the hydrocarbon charge stock, maintaining thecharge stock substantially free of sulfur is ordinarily sufficient toensure that the environment containing the catalyst is maintained in thesubstantially sulfur-free state. More specifically, since hydrogen is amajor product of the dehydrocyclization process, ordinarily the inputdiluent stream required for the process is obtained by recycling aportion of the hydrogen-rich stream recovered from the effluentwithdrawn from the dehydrocyclization zone. In this typical situation,this recycle hydrogen stream will ordinarily be substantially free ofsulfur if the charge stock is maintained free of sulfur. If autogenoushydrogen is not utilized as the diluent, then, of course, the concept ofthe present invention requires that the input diluent stream bemaintained substantially sulfur-free; that is, less than 10 vol. ppm. ofH₂ S, preferably less than 5 vol. ppm., and most preferably less than 1vol. ppm.

The only other possible sources of sulfur that could interfere with theperformance of the instant catalyst are sulfur that is initiallycombined with the catalyst and/or with the plant hardware. As indicatedhereinbefore, a highly preferred feature of the present acidicmulti-metallic catalyst is that it is maintained in a substantiallysulfur-free state; therefore, sulfur released from the catalyst is notusually a problem in the present process. Hardware sulfur is ordinarilynot present in a new plant; it only becomes a problem when the presentprocess is to be implemented in a plant that has seen service with asulfur-containing feed stream. In this latter case, the preferredpractice of the present invention involves an initial pretreatment ofthe sulfur-containing plant in order to remove substantially all of thedecomposable hardware sulfur therefrom. This can be easily accomplishedby any of the techniques for stripping sulfur from hardware known tothose in the art; for example, by the circulation of a substantiallysulfur-free hydrogen stream through the internals of the plant at arelatively high temperature of about 800° to about 1200° F. until the H₂S content of the effluent gas stream drops to a relatively low level --typically, less than 5 vol. ppm. and preferably less than 2 vol. ppm. Insum, the preferred sulfur-free feature of the present invention requiresthat the total amount of detrimental sulfur entering thedehydrocyclization zone containing the hereinbefore described acidicmultimetallic catalyst must be continuously maintained at asubstantially low level; specifically, the amount of sulfur must be heldto a level equivalent to less than 10 wt. ppm., and preferably less than1 wt. ppm., of the feed.

In the case where the sulfur content of the charge stock for the presentprocess is greater than the amounts previously specified, it is, ofcourse, necessary to treat the charge stock in order to remove theundesired sulfur contaminants therefrom. This is easily accomplished byusing any one of the conventional catalytic pretreatment methods such ashydrorefining, hydrotreating, hydrodesulfurization, and the like toremove substantially all sulfurous, nitrogenous, and water-yieldingcontaminants from this feed stream. Ordinarily, this involves subjectingthe sulfur-containing feed stream to contact with a suitablesulfur-resistant hydrorefining catalyst in the presence of hydrogenunder conversion conditions selected to decompose sulfur contaminantscontained therein and form hydrogen sulfide. The hydrorefining catalysttypically comprises one or more of the oxides or sulfides of thetransition metals of Groups VI and VIII of the Periodic Table. Aparticularly preferred hydrorefining catalyst comprises a combination ofa metallic component from the iron group metals of Group VIII and of ametallic component of the Group VI transition metals combined with asuitable porous refractory support. Particularly good results have beenobtained when the iron group component is cobalt and/or nickel and theGroup VI transition metal is molybdenum or tungsten. The preferredsupport for this type of catalyst is a refractory inorganic oxide of thetype previously mentioned. For example, good results are obtained with ahydrorefining catalyst comprising cobalt oxide and molybdenum oxidesupported on a carrier material comprising alumina and silica. Theconditions utilized in this hydrorefining step are ordinarily selectedfrom the following ranges: a temperature of about 600° to about 950° F.,a pressure of about 500 to about 5000 psig., a liquid hourly spacevelocity of about 1 to about 20 hr.⁻¹, and a hydrogen circulation rateof about 500 to about 10,000 standard cubic feet of hydrogen per barrelof charge. After this hydrorefining step, the hydrogen sulfide, ammonia,and water liberated therein, are then easily removed from the resultingpurified charge stock by conventional means such as a suitable strippingoperation. Specific hydrorefining conditions are selected from theranges given above as a function of the amounts and kinds of the sulfurcontaminants in the feed stream in order to produce a substantiallysulfur-free charge stock which is then charged to the process of thepresent invention.

It is also generally preferred to utilize the novel acidic multimetalliccatalytic composite in a substantially water-free environment. Essentialto the achievement of this condition in the dehydrocyclization zone isthe control of the water level present in the charge stock and thediluent stream which is being charged to the zone. Best results areordinarily obtained when the total amount of water entering theconversion zone from any source is held to a level less than 20 ppm. andpreferably less than 5 ppm. expressed as weight of equivalent water inthe charge stock. In general, this can be accomplished by carefulcontrol of the water present in the charge stock and in the diluentstream. The charge stock can be dried by using any suitable drying meansknown to the art, such as a conventional solid adsorbent having a highselectivity for water, for instance, sodium or calcium crystallinealuminosilicates, silica gel, activated alumina, molecular sieves,anhydrous calcium sulfate, high surface area sodium, and the likeadsorbents. Similarly, the water content of the charge stock may beadjusted by suitable stripping operations in a fractionation column orlike device. And in some cases, a combination of adsorbent drying anddistillation drying may be used advantageously to effect almost completeremoval of water from the charge stock. In an especially preferred modeof operation, the charge stock is dried to a level corresponding to lessthan 5 wt. ppm. of H₂ O equivalent. In general, it is preferred tomaintain the diluent stream entering the hydrocarbon conversion zone ata level of about 10 vol. ppm. of water or less and most preferably about5 vol. ppm. or less. If the water level in the diluent stream is toohigh, drying of same can be conveniently accomplished by contacting thisstream with a suitable desiccant such as those mentioned above.

The dehydrocyclization conditions used in the present method include areactor pressure which is selected from the range of about 0 psig. toabout 250 psig., with the preferred pressure being about 50 psig. toabout 150 psig. In fact, it is a singular advantage of the presentinvention that it allows stable operation at lower pressure than haveheretofore been successfully utilized in dehydrocyclization system withall platinum monometallic catalysts. In other words, the acidicmulti-metallic catalyst of the present invention allows the operation ofa dehydrocyclization system to be conducted at lower pressure for aboutthe same or better catalyst cycle life before regeneration as has beenheretofore realized with conventional monometallic catalysts at higherpressure.

The temperature required for dehydrocyclization with the instantcatalyst is markedly lower than that required for a similar operationusing a high quality catalyst of the prior art. This significant anddesirable feature of the present invention is a consequence of theextraordinary activity of the acidic multimetallic catalyst of thepresent invention for the dehydrocyclization reaction. Hence, thepresent invention requires a temperature in the range of from 800° F. toabout 1100° F. and preferably about 850° F. to about 1000° F. As is wellknown to those skilled in the dehydrocyclization art, the initialselection of the temperature within this broad range is made primarilyas a function of the desired conversion level of the dehydrocyclizationhydrocarbon considering the characteristics of the charge stock and ofthe catalyst. Ordinarily, the temperature then is thereafter slowlyincreased during the run to compensate for the inevitable deactivationthat occurs to provide a relatively constant value for conversion.Therefore, it is a feature of the present invention that not only is theinitial temperature requirement substantially lower, but also the rateat which the temperature is increased in order to maintain a constantconversion level is substantially lower for the catalyst of the presentinvention than for an equivalent operation with a high qualitydehydrocyclization catalyst which is manufactured in exactly the samemanner as the catalyst of the present invention except for the inclusionof the cobalt and lanthanide series components. Moreover, for thecatalyst of the present invention, the aromatic yield loss for a giventemperature increase is substantially lower than for a high qualitydehydrocyclization catalyst of the prior art.

The liquid hourly space velocity (LHSV) used in the instantdehydrocyclization method is selected from the range of about 0.1 toabout 5 hr.⁻¹, with a value in the range of about 0.3 to about 2 hr.⁻¹being preferred. In fact, it is a feature of the present invention thatit allows operations to be conducted at higher LHSV than normally can bestably achieved in a dehydrocyclization process with a high qualitydehydrocyclization catalyst of the prior art. This last feature is ofimmense economic significance because it allows a dehydrocyclizationprocess to operate at the same throughput level with less catalystinventory or at greatly increased throughput level with the samecatalyst inventory than that heretofore used with conventionaldehydrocyclization catalysts at no sacrifice in catalyst life beforeregeneration.

The following working examples are given to illustrate further thepreparation of the acidic multimetallic catalytic composite used in thepresent invention and the beneficial use thereof in thedehydrocyclization of hydrocarbons. It is understood that the examplesare intended to be illustrative rather than restrictive.

These examples are all performed in a laboratory scaledehydrocyclization plant comprising a reactor, a hydrogen separatingzone, heating means, cooling means, pumping means, compressing means,and the like conventional equipment. In this plant, a sulfur-free feedstream containing the dehydrocyclizable hydrocarbon is combined with ahydrogen recycle stream and the resultant mixture heated to the desiredconversion temperature, which refers herein to the temperaturemaintained at the inlet to the reactor. The heated mixture is thenpassed into contact with the instant acidic multimetallic catalyst whichis maintained in a sulfur-free and water-free environment and which ispresent as a fixed bed of catalyst particles in the reactor. Thepressures reported herein are recorded at the outlet from the reactor.An effluent stream is withdrawn from the reactor, cooled, and passedinto the hydrogen-separating zone wherein a hydrogen-containing gasphase separates from a hydrocarbon-rich liquid phase containing aromatichydrocarbons, unconverted dehydrocyclizable hydrocarbons, andby-products of the dehydrocyclization reaction. A portion of thehydrogen-containing gas phase is recovered as excess recycle gas and theremaining portion is passed through a high surface area sodium scrubberand the resulting substantially water-free and sulfur-free hydrogenstream is recycled through suitable compressing means to the heatingzone as described above. The hydrocarbon-rich liquid phase from theseparating zone is withdrawn therefrom and subjected to analysis todetermine conversion and selectivity for the desired aromatichydrocarbon as will be indicated in the Examples. Conversion numbers ofthe dehydrocyclizable hydrocarbon reported herein are all calculated onthe basis of disappearance of the dehydrocyclizable hydrocarbon and areexpressed in weight percent. Similarly, selectivity numbers are reportedon the basis of weight of desired aromatic hydrocarbon produced per 100weight parts of dehydrocyclizable hydrocarbon charged.

All of the catalysts utilized in these examples are prepared accordingto the following general method with suitable modification instoichiometry to achieve the compositions reported in each example.First, an alumina carrier material comprising 1/16 inch spheres havingan apparent bulk density of about 0.5 g/cc is prepared by: forming analuminum hydroxy chloride sol by dissolving substantially pure aluminumpellets in a hydrochloric acid solution, adding hexamethylenetetramineto the resulting alumina sol, gelling the resulting solution by droppingit into an oil bath to form spherical particles of an alumina hydrogel;aging, and washing the resulting particles with an ammoniacal solutionand finally drying and calcining the aged and washed particles to formspherical particles of gamma-alumina containing about 0.3 wt. % combinedchloride. Additional details as to this method of preparing this aluminacarrier material are given in the teachings of U.S. Pat. No. 2,620,314.

The resulting gamma-alumina particles are then contacted at suitableimpregnation conditions with an aqueous impregnation solution containingchloroplatinic acid, neodymium nitrate, cobaltous chloride and hydrogenchloride. The amounts of metallic reagents contained in thisimpregnation solution are carefully adjusted to yield a finalmultimetallic catalytic composite containing a uniform dispersion of thehereinafter specified amounts of platinum, neodymium and cobalt. Thehydrochloric acid is utilized in an amount of about 12 wt. % of thealumina particles. In order to ensure a uniform dispersion of the metalmoieties in the carrier material, the impregnation solution ismaintained in contact with the carrier material particles for about 1/2to about 3 hours at a temperature of about 70° F. with constantagitation. The impregnated spheres are then dried at a temperature ofabout 225° F. for about an hour and thereafter calcined or oxidized witha sulfur-free dry air stream at a temperature of about 930° F. and aGHSV of about 500 hr.⁻¹ for about 1/2 hour effective to convertsubstantially all of the metallic components to the corresponding oxideforms. In general, it is a good practice to thereafter treat theresulting oxidized particles with a sulfur-free air stream containing H₂O and HCl in a mole ratio of about 30:1 at a temperature of about 930°F. for an additional period of about 2 hours in order to adjust thecombined chloride contained in the catalyst to a value of about 1 wt. %.The halogen-treated spheres are next subjected to a second oxidationstep with a dry sulfur-free air stream at 930° F. and a GHSV of 500hr.⁻¹ for an additional period of about 1/2 hour. The resulting oxidizedand halogen-treated particles are thereafter subjected to a dryprereduction treatment designed, as pointed out hereinafter, to reducesubstantially all of the platinum component to the elemental metallicstate, while maintaining substantially all of the neodymium component ina positive oxidation state. This step involves contacting the catalystparticles with a substantially sulfur-free and hydrocarbon-free hydrogenstream containing less than 5 vol. ppm. of H₂ O at a temperature of 930°F., atmospheric pressure and a GHSV of about 400 hr.⁻¹ for a period ofabout 1 hour.

EXAMPLE I

The reactor is loaded with 100 cc of an acidic catalyst containing, onan elemental basis, 0.3 wt. % platinum, 1.0 wt. % cobalt, and 1.0 wt. %neodymium, and about 1 wt. % chloride. This corresponds to an atomicratio of cobalt to platinum of 11:1 and of neodymium to platinum of4.5:1. The feed stream utilized is commercial grade n-hexane. The feedstream is contacted with the catalyst at a temperature of 920° F., apressure of 125 psig., a liquid hourly space velocity of 0.75 hr.⁻¹, anda hydrogen-containing recycle gas to hydrocarbon mole ratio of 4:1. Thedehydrocyclization plant is lined-out at these conditions and a 20 hourtest period commenced. The hydrocarbon product stream from the plant iscontinuously analyzed by GLC (gass liquid chromatography) and about a90% conversion of n-hexane is observed with a selectivity for benzene ofabout 25%.

EXAMPLE II

The acidic catalyst contains, on an elemental basis, 0.375 wt. %platinum 0.5 wt. % cobalt, 0.4 wt. % neodymium and about 1 wt. %combined chloride. For this catalyst, the pertinent atomic ratios are:cobalt to platinum = 4.41:1 and neodymium to platinum = 1.44:1. The feedstream is commercial grade normal heptane. The dehydrocyclizationreactor is operated at a temperature of 900° F., a pressure of 125psig., a liquid hourly space velocity of 0.75 hr.⁻¹, and a recycle gasto hydrocarbon mole ratio of 5:1. After a line-out period, a 20 hourtest period is performed during which the average conversion of then-heptane is maintained at about 95% with a selectivity for aromatics (amixture of toluene and benzene) of about 45%.

EXAMPLE III

The acidic catalyst is the same as utilized in Example II. The feedstream is normal octane. The conditions utilized are a temperature of880° F., a pressure of 125 psig., a liquid hourly space velocity of 0.75hr.⁻¹, and a recycle gas to hydrocarbon mole ratio of 4:1. After aline-out period, a 20 hour test shows an average conversion of about100% and a selectivity for aromatics of about 50%.

EXAMPLE IV

The acidic catalyst contains, on an elemental basis, 0.6 wt. % platinum,1.0 wt. % cobalt, 1.0 wt. % neodymium and about 1 wt. % combinedchloride. On an atomic basis, the ratio of cobalt to platinum is 5.52:1and the ratio of neodymium to platinum is 2.3:1. The feed stream is a50/50 mixture of n-hexane and n-heptane. The conditions utilized are atemperature of 945° F., a pressure of 125 psig., a liquid hourly spacevelocity of 0.75 hr.⁻¹, and a recycle gas to hydrocarbon mole ratio of5:1. After a line-out period, a 20 hour test is performed with aconversion of about 100% and a selectivity for aromatics of about 45%.The selectivity for benzene and toluene are about 20% and 25%,respectively.

It is intended to cover by the following claims, all changes andmodifications of the above disclosure of the present invention whichwould be self-evident to a man of ordinary skill in thecatalyst-formulation art or in the hydrocarbon dehydrocyclization art.

I claim as my invention:
 1. A method for dehydrocyclizing adehydrocyclizable hydrocarbon comprising contacting the hydrocarbon atdehydrocyclization conditions with an acidic catalytic compositecomprising a porous carrier material containing, on an elemental basis,about 0.01 to about 2 wt. % platinum group metal, about 0.05 to about 5wt. % cobalt, about 0.01 to about 5 wt. % lanthanide series metal andabout 0.1 to about 3.5 wt. % halogen; wherein the platinum group metal,catalytically available cobalt and lanthanide series metal are uniformlydispersed throughout the porous carrier material; wherein substantiallyall of the platinum group metal is present in the elemental metallicstate; wherein substantially all of the lanthanide series metal ispresent in an oxidation state above that of the elemental metal; andwherein substantially all of the catalytically available cobalt ispresent in the elemental metallic state or in a state which is reducibleto the elemental metallic state under dehydrocyclization conditions orin a mixture of these states.
 2. A method as defined in claim 1 whereinthe dehydrocyclizable hydrocarbon is admixed with hydrogen when itcontacts the catalytic composite.
 3. A method as defined in claim 1wherein the platinum group metal is platinum.
 4. A method as defined inclaim 1 wherein the platinum group metal is palladium.
 5. A method asdefined in claim 1 wherein the platinum group metal is iridium.
 6. Amethod as defined in claim 1 wherein the platinum group metal isrhodium.
 7. A method as defined in claim 1 wherein the lanthanide seriesmetal is neodymium.
 8. A method as defined in claim 1 wherein thelanthanide series metal is cerium.
 9. A method as defined in claim 1wherein the lanthanide series metal is lanthanum.
 10. A method asdefined in claim 1 wherein the porous carrier material is a refractoryinorganic oxide.
 11. A method as defined in claim 10 wherein therefractory inorganic oxide is alumina.
 12. A method as defined in claim1 wherein the halgoen is combined chloride.
 13. A method as defined inclaim 1 wherein the dehydrocyclizable hydrocarbon is an aliphatichydrocarbon containing 6 to 20 carbon atoms per molecule.
 14. A methodas defined in claim 13 wherein the aliphatic hydrocarbon is an olefin.15. A method as defined in claim 13 wherein the aliphatic hydrocarbon isa paraffin.
 16. A method as defined in claim 15 wherein the paraffinhydrocarbon is a paraffin containing 6 to 10 carbon atoms per molecule.17. A method as defined in claim 15 wherein the paraffin is hexane. 18.A method as defined in claim 15 wherein the paraffin is heptane.
 19. Amethod as defined in claim 15 wherein the paraffin is octane.
 20. Amethod as defined in claim 15 wherein the paraffin is nonane.
 21. Amethod as defined in claim 15 wherein the paraffin is a mixture of C₆ toC₉ paraffins.
 22. A method as defined in claim 1 wherein thedehydrocyclizable hydrocarbon is contained in a naphtha fraction boilingin the range of about 140° F. to about 400° F.
 23. A method as definedin claim 2 wherein the dehydrocyclization conditions include atemperature of 800 to about 1100° F., a pressure of 0 to 250 psig. aLHSV of 0.1 to 5 hr.⁻¹, and a hydrogen to hydrocarbon mole ratio ofabout 0.1:1 to about 10:1.
 24. A method as defined in claim 1 whereinthe acidic catalytic composite contains, on an elemental basis, about0.05 to about 1 wt. % platinum group metal, about 0.1 to about 2.5 wt. %cobalt and about 0.05 to about 2 wt. % lanthanide series metal and about0.5 to about 1.5 wt. % halogen.
 25. A method as defined in claim 1wherein the metals content of the catalytic composite is adjusted sothat the atomic ratio of lanthanide series metal to platinum group metalis about 0.1:1 to about 20:1 and the atomic ratio of cobalt to platinumgroup metal is about 0.1:1 to about 66:1.
 26. A method as defined inclaim 1 wherein the contacting is performed in a substantiallywater-free environment.
 27. A method as defined in claim 1 wherein thecontacting is performed in a substantially sulfur-free environment. 28.A method as defined in claim 1 wherein substantially all of thecatalytically available cobalt contained in the composite is present inthe elemental metallic state after the method is started-up andlined-out at dehydrocyclization conditions.
 29. A method as defined inclaim 1 wherein substantially all of the lanthanide series metal ispresent in the catalytic composite in the form of the correspondingoxide.
 30. A method as defined in claim 1 wherein the catalyticcomposite is in a sulfur-free state.